How does Gizoogle.net work? (Not the language-processing but the "copy-cating")

[Miguel Valencia via StackOverflow]

I want to do something like gizoogle, where a complete, intact, webpage from a different domain is displayed on on my site.

It was suggested to me that I should set up a proxy server. I found directions for setting up a proxy server using Google App Engine, but how do I modify the content? I've tried searching for phrases like "How to modify output from a proxy server before reaching the client," but so far no luck. The terms I've been offered so far (outside of Stack Overflow) aren't working. If someone can suggest some terms that point me in the right direction, I'd mark this as "answered."

I'm pretty sure I could do what I want if I understood how Gizoogle.net worked—not the language processing aspect of it but merely the aspect that pulls Google results and displays webpages without hindering the page's original functionality. So if someone knows how that aspect of gizoogle works, I would mark this as "answered" and appreciate if you said, "It looks like Gizoogle works by using such-and-such technologies to pull in a web page without ruining the page's original functionality. Check those out."

Framesets seems like an option. I will continue development using those if no alternative is found, but I can tell Gizoogle doesn't use framesets (none are visible when viewing the source) so I would rather figure out how Gizoogle functions.

All ideas appreciated! :)

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UPDATE: This Stack Overflow question seems to point me in the right direction.

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